The capability of delivering biologically active molecules to plant and animal cells is of great importance to medicine and genetic research and engineering. In medicine, for example, the development of effective vaccines requires systems for providing characteristic portions of infectious biological entities to immune system cells so that the immune system will recognize and fight an infection. When such characteristic portions (antigens) of entities such as viruses, bacteria or even tumors are appropriately provided, the immune systems identifies the antigens as foreign and stimulates development of immunological countermeasures. One way to provide antigens is to deliver them directly into cells. Another way is to deliver to the cells DNA sequences that encode the antigens.
Gene therapy seeks to introduce additional genetic material (typically DNA) into a cell in such a way that the additional genetic material will be functionally incorporated into the existing genetic material of the cell. For example, there are certain diseases that are caused by the absence in cells of normally present DNA sequences (genes) needed to make critical proteins. Gene therapy seeks to alleviate such diseases by providing the cells with the missing DNA sequences so that the cells themselves can provide the critical proteins. To achieve this goal, the missing DNA sequences need to be introduced into cells in such a fashion that they are functionally incorporated into the genetic material and mechanisms of the cells.
The effectiveness of an active biological molecule in a cell often can be enhanced by the presence of one or more additional different molecules. For example, there are molecules, called adjuvants, that will increase the likelihood that an antigen will be recognized as an appropriate target for immunological countermeasures. As another example, there are also molecules that will interact with cell receptors and increase the likelihood of incorporation into the cell. Such enhancing molecules, however, typically must be close to the active molecule in order to enhance its effectiveness.
Conventional approaches to delivering biological molecules to cells leave much to be desired. The common approach to gene therapy is based on the fact that viruses have evolved to inject genetic material into a cell and use the cell's genetic machinery to replicate the viral genetic material. Appropriate modification of the virus might eliminate its harmful features and redirect a viral vector to deliver desirable genetic material into the cell. However virus vectors often generate counterproductive host immune responses and present a risk of killing infected host cells (cytotoxicity).
Other delivery approaches that have been suggested include the use of carriers comprising liposomes, polymers and gold nanoparticles. They have not, however, achieved notable success in efficiently incorporating new genetic material or in making more effective vaccines. Accordingly there Is a need for improved methods and products for delivering biological molecules to cells.